Field of the Invention
Technology described herein generally relates to deposition of metals by PECVD. Specifically, technology described herein generally relates to methods of depositing ruthenium and avoiding corrosion on an underlying layer.
Description of the Related Art
Ruthenium (Ru) has been considered for decades as a candidate material for copper (Cu) metallization for its excellent properties of copper seed enhancement, resistance to oxidation. The wetting properties that ruthenium metallization provides to Cu, especially when feature sizes gets smaller, is of particular importance.
Chemical Vapor Deposition (CVD) has been a main approach to deposit ruthenium. CVD is well known in the art to provide better control of film morphology and step coverage over other methods, such as Physical Vapor Deposition (PVD). These benefits are increasingly important as feature move below the 35 nm range. Despite many superior aspects of CVD methods generally, prior techniques have not been successful at depositing ruthenium on certain underlying layers, such as copper layers.
CVD deposition of ruthenium on copper seed layers causes void formation in underlying copper layers as the layer is exposed to the ruthenium precursor and the deposited ruthenium. This phenomenon happens during the deposition step of ruthenium and is generally observed as ulcerations in the underlying copper materials. Stated another way, when ruthenium is deposited on top of copper or thin barriers including Ta or TaN, voids typically form in the copper layer exposed to the CVD ruthenium process either during deposition or during the H2 annealing step followed by deposition. Others have worked around this problem by depositing a thicker copper seed layer prior to ruthenium CVD. However, thicker layers create scaling problems for features below 40 nm.
Thus, there is a need in the art for depositing ruthenium on thin metals layers to achieve the benefits of ruthenium without the deleterious effects described above.